Magnetic tape media having servo patterns

ABSTRACT

Magnetic tape media according to one embodiment includes a servo track having a plurality of servo marks therealong. A distance of the servo marks, as originally written, from an edge of the tape media varies along the length of the magnetic tape media. Magnetic tape media according to another embodiment includes a plurality of servo tracks having physical characteristics of being written by an apparatus that monitors a lateral position of the magnetic tape media passing over a servo writing head during a servo track writing operation and writes servo marks to the magnetic tape media. A timing of the writing of each servo mark is based on the monitored position of the magnetic tape media.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/141,363, filed Jun. 18, 2008, which is herein incorporated byreference.

BACKGROUND

The present invention relates to data storage, and more particularly,this invention relates to systems and methods for writing servo patternson a magnetic data storage medium, and the resulting media.

In magnetic storage systems, data is read from and written onto magneticrecording media utilizing magnetic transducers commonly. Data is writtenon the magnetic recording media by moving a magnetic recordingtransducer to a position over the media where the data is to be stored.The magnetic recording transducer then generates a magnetic field, whichencodes the data into the magnetic media. Data is read from the media bysimilarly positioning the magnetic read transducer and then sensing themagnetic field of the magnetic media. Read and write operations may beindependently synchronized with the movement of the media to ensure thatthe data can be read from and written to the desired location on themedia.

In a tape drive system, magnetic tape is moved over the surface of thetape head at high speed. This movement generally entrains a film of airbetween the head and tape. Usually the tape head is designed to minimizethe spacing between the head and the tape. The spacing between themagnetic head and the magnetic tape is crucial so that the recordinggaps of the transducers, which are the source of the magnetic recordingflux, are in near contact with the tape to effect efficient signaltransfer, and so that the read element is in near contact with the tapeto provide effective coupling of the magnetic field from the tape to theread element.

Magnetic tape may use a written servo pattern to indicate lateralposition on tape. This servo pattern is used to indicate lateralposition, on tape, of the various written tracks. The servo pattern isnot perfect due to variations in tape velocity and lateral position inthe servo writer during servo writing. This can partly be attributed tothe inability of most mechanical head positioning motors to react totape lateral position changes fast enough to move the head into properposition to write the servo pattern. The component of the servo patterndue to the velocity variations and lateral motion is termed the ‘writtenin’ component and limits the accuracy of the track-following actuator inthe drive. This is due to the high frequency components of the ‘writtenin’ servo which the track-following actuator has difficulty infollowing. Greater track-following accuracy becomes more important aswritten tracks get narrower. Hence ‘written in’ servo noise limits theultimate track pitch attainable in magnetic tape recording.

SUMMARY OF THE INVENTION

Magnetic tape media according to one embodiment includes a servo trackhaving a plurality of servo marks therealong. A distance of the servomarks, as originally written, from an edge of the tape media variesalong the length of the magnetic tape media.

Magnetic tape media according to another embodiment includes a pluralityof servo tracks having physical characteristics of being written by anapparatus that monitors a lateral position of the magnetic tape mediapassing over a servo writing head during a servo track writing operationand writes servo marks to the magnetic tape media. A timing of thewriting of each servo mark is based on the monitored position of themagnetic tape media.

A method for writing a servo track according to another embodimentcomprises optically monitoring a lateral position of a magnetic tapepassing over a servo writing head during a servo track writingoperation; monitoring a velocity of the magnetic tape relative to thehead; writing servo marks to the magnetic tape, wherein the servo marksare magnetically defined bars arranged in base sets, each base setcomprising at least two bars oriented at different angles with respectto a direction of tape travel; adjusting a timing of the writing of eachmark based on the monitored position of the magnetic tape; and furtheradjusting the timing of the writing of each mark based on the monitoredvelocity of the magnetic tape.

A method for writing a servo track according to yet another embodimentcomprises reading a previously-written servo pattern on a magnetic tape;monitoring a lateral position of a magnetic tape during the reading;deducing written in noise in the servo pattern; and writing servo marksto the magnetic tape over the written in noise.

A system for writing a servo track according to one embodiment comprisesa servo writing head for writing servo marks onto a magnetic tape; adevice for optically monitoring a position of the magnetic tape during aservo track writing operation; and a controller for controlling a timingof the writing of the servo marks to the magnetic tape based on themonitored position of the magnetic tape.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1 illustrates a flat-lapped magnetic tape head, in accordance withone embodiment of the present invention.

FIG. 2A is a tape bearing surface view taken from Line 2A of FIG. 1.

FIG. 2B is a detailed view taken from Circle 2B of FIG. 2A.

FIG. 3A is a representative diagram of a servo pattern according to oneembodiment of the present invention.

FIG. 3B illustrates a magnetic tape having servo patterns of differentcharacteristics according to the positioning of the magnetic tape asdetermined by an optical detector according to one embodiment of thepresent invention.

FIG. 4 is a schematic diagram of a tape drive system according to oneembodiment of the present invention.

FIG. 5 is a flow diagram of a process according to one embodiment of thepresent invention.

FIG. 6 is a flow diagram of a process according to one embodiment of thepresent invention.

FIG. 7 is a flow diagram of a process according to one embodiment of thepresent invention.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

The following description discloses several preferred embodiments oftape-based storage systems, as well as operation and/or component partsthereof.

In one general embodiment, a method for writing a servo track comprisesmonitoring a lateral position of a magnetic tape passing over a servowriting head during a servo track writing operation and writing servomarks to the magnetic tape, a timing of the writing of each mark beingbased on the monitored position of the magnetic tape.

In another general embodiment, a method for writing a servo trackcomprises optically monitoring a lateral position of a magnetic tapepassing over a servo writing head during a servo track writing operationand monitoring a velocity of the magnetic tape relative to the head.Also, this method includes writing servo marks to the magnetic tape,wherein the servo marks are magnetically defined bars arranged in basesets, each base set comprising at least two bars oriented at differentangles with respect to a direction of tape travel. In addition, thismethod includes adjusting a timing of the writing of each mark based onthe monitored position of the magnetic tape and further adjusting thetiming of the writing of each mark based on the monitored velocity ofthe magnetic tape.

In another general embodiment, a method for writing a servo trackcomprises reading a previously-written servo pattern on a magnetic tapeand monitoring a lateral position of a magnetic tape during the reading.Also, this method includes deducing written in noise in the servopattern and writing servo marks to the magnetic tape over the written innoise.

In another general embodiment, a system for writing a servo trackcomprises a servo writing head for writing servo marks onto a magnetictape. Also, this system includes a device for optically monitoring aposition of the magnetic tape during a servo track writing operation anda controller for controlling a timing of the writing of the servo marksto the magnetic tape based on the monitored position of the magnetictape.

FIG. 1 illustrates a flat-lapped bi-directional, two-module magnetictape head 100, in accordance with one embodiment of the presentinvention. As shown, the head includes a pair of bases 102, eachequipped with a module 104. The bases may be “U-beams” that areadhesively coupled together. Each module 104 includes a substrate 104Aand a closure 104B with readers and writers 106 situated therebetween.In use, a tape 108 is moved over the modules 104 along a tape bearingsurface 109 in the manner shown for reading and writing data on the tape108 using the readers and writers 106. Conventionally, a partial vacuumis formed between the tape 108 and the tape bearing surface 109 formaintaining the tape 108 in close proximity with the readers and writers106.

The substrates 104A are typically constructed of a wear resistantmaterial, such as a ceramic. The closures 104B may be made of the sameor similar ceramic as the substrates 104A.

The readers and writers 106 may be arranged in a piggybackconfiguration. The readers and writers 106 may also be arranged in aninterleaved configuration. Alternatively, each array of channels may bereaders or writers only. Any of these arrays may contain one or moreservo readers.

FIG. 2A illustrates the tape bearing surface 109 of one of the modules104. A representative tape 108 is shown in dashed lines. The module 104is preferably long enough to be able to support the tape as the headsteps between data bands.

In this example, the tape 108 includes 4-22 data bands, e.g., with 16data bands and 17 servo tracks 202, as shown in FIG. 2A on a one-halfinch wide tape 108. The data bands are defined between servo tracks 202.Each data band may include a number of data tracks, for example 96 datatracks (not shown). During read/write operations, the elements 106 arepositioned within one of the data bands. Outer readers, sometimes calledservo readers, read the servo tracks 202. The servo signals are in turnused to keep the elements 106 aligned with a particular track during theread/write operations.

FIG. 2B depicts a plurality of read and/or write elements 106 formed ina gap 208 on the module 104 of FIG. 2A. As shown, the array of elements106 includes, for example, 16 writers 209, 16 readers 210 and two servoreaders 212, though the number of elements may vary. Illustrativeembodiments include 8, 16, 32, and 64 elements per array 106. Apreferred embodiment includes 24 readers per array and/or 24 writers perarray. This allows the tape to travel more slowly, thereby reducingspeed-induced tracking and mechanical difficulties. While the readersand writers may be arranged in a piggyback configuration as shown inFIG. 2B, the readers 210 and writers 209 may also be arranged in aninterleaved configuration. Alternatively, each array of elements 106 maybe readers or writers only, and the arrays may contain one or more servoreaders. As noted by considering FIGS. 1 and 2A-B together, each module104 may include a complementary set of elements 106 for such things asbi-directional reading and writing, read-while-write capability, etc.

In preferred embodiments, the width of the servo head is such thattransition broadening effects are minimized. Giant Magnetoresistive(GMR) and Tunneling Magnetoresistive (GMR) devices are preferably usedin servo readers for advanced formats which require servo readers havingsmall track widths such as 0.5 micrometers.

A typical servo track in one embodiment, shown in FIG. 3A, includesrepeating servo patterns 302. A typical servo pattern 302 includes oneor more magnetically-defined base sets 304 (e.g., in a chevron shape:/\) of two or more magnetically-defined bars 306, which may be writtenconcurrently. Servo patterns 302 may include groups of the base sets 304nested with one another (e.g., ///\\\). In one embodiment of the presentinvention, the distance between the first bar in a group and the firstbar in the next group, b, is equal to two times the distance between abase set, a. Note that the chevron-type servo pattern is one of manythat can be used in various embodiments of the present invention. Otherillustrative servo patterns include “M” type (/\/\, |\/|, /|\, etc.),“N” type (/\/\, |\|, /|/, etc.), etc. The M or N type patterns may bepreferable to simple two-bar chevron type servo patterns in someinstances, such as where the N or M pattern contain parallel bars,thereby allowing the system to calculate more accurately a velocity ofthe tape.

Variations and combinations of the foregoing types of servo base setsare also possible. Also note that the bars need not all have identicaldirect or inverse angles.

For properly recording a servo pattern on a magnetic tape that willaccount for tape velocity and lateral position changes, the lateralposition and velocity of the magnetic tape should be known.

As is well known the lateral position, y, indicated by the measurementsof the times, t_(a) and t_(b) is given by Equation 1:

$\begin{matrix}{y = \frac{\left\lbrack {{\left( {t_{a}/t_{b}} \right)b_{0}} - a_{0}} \right\rbrack}{2\tan\;\theta}} & {{Equation}\mspace{14mu} 1}\end{matrix}$where a₀ and b₀ are the distances between oppositely angled and paralleltransitions respectively in the center of the servo band, a and b arethe distances between oppositely angled and parallel transitions at aposition y above or below the centerline, θ is the angle of the servomark relative to the vertical, t_(a) is the time it takes the magnetictape to travel the distance of a, and t_(b) is the time it takes themagnetic tape to travel the distance of b. An exemplary angle θ is inthe range of >0° to about 10°, e.g., about 4° to about 6°.

To compensate for tape lateral motion of ΔY and an average velocity ofV, the second transition (forming the a distance) is preferably delayedby:

$\begin{matrix}{{\Delta\; t} = \frac{\Delta\; Y\;\tan\;\theta}{\overset{\_}{V}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$where the two generating gaps are separated by a₀ at the center of theservo band. Thus, for example, assuming θ=6°, if the tape moves up(toward the apex of the inverted V) by 2 microns, at a tape velocity of4 meters per second, then the second transition is delayed by 52.55nanoseconds.

The detection of the lateral motion and the velocity of the tape can bemade optically through edge detection, interferometry at the tape edge,or laser Doppler anemometry of the tape surface.

Alternatively, the velocity of the tape can be determined by measuringthe period of a series of high frequency timing marks previously writtenon the tape. Alternatively, a previously written servo pattern can bemeasured to deduce the written-in component and re-written to remove it.A series of servo readers in close proximity can be used to determinethe written-in component, since for closely spaced servo readers, thelateral motion of the tape appears equally to all servo readers. Thecomponent of lateral motion that propagates with the velocity of thetape is due to the written-in servo marks and can be removed. Thelateral motion as determined by each of the servo readers is comprisedof two parts, one that appears equally to all readers and anothercomponent that appears time-shifted due to the propagation of thewritten-in mark. This time shift is:

$\begin{matrix}{T = \frac{\Delta\; X}{\overset{\_}{V}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$where ΔX is the distance between servo readers. Various methods, wellknown in the art, may be used to estimate the written-in component andthis is subtracted from the lateral motion of the servo readers to yieldan improved measurement of the lateral motion. This determination of thelateral motion is used in the equation above to re-servo write the servoband.

Another method to re-servo write tape reduces or eliminatestrack-following error. A previously written servo pattern is read anddecoded to determine the lateral motion. This data is used to simulatethe actuator response. The difference between the actuator response andthe actual decoded lateral motion is the position error signal. Thisdifference is removed from the lateral position that is re-servo writtenonto the tape, eliminating or reducing the track-following error.

In another approach, and with reference to FIG. 3A, the lateralposition, when b=2a, may be given by Equation 4:

$\begin{matrix}{y = {\frac{a}{2\tan\;\theta}\left\lbrack {1 - {2\frac{t_{a}}{t_{b}}}} \right\rbrack}} & {{Equation}\mspace{14mu} 4}\end{matrix}$where y is the lateral position, a is the distance between a base set, bis the distance between servo mark groups, θ is the angle off verticalof the servo mark, t_(a) is the time it takes the magnetic tape totravel the distance of a, and t_(b) is the time it takes the magnetictape to travel the distance of b.

In various embodiments, the angle θ (defined between a bar and aperpendicular line to the edge of the magnetic tape) is increased,thereby allowing a faster servo pattern repetition rate.

When a servo reader follows servo marks on a magnetic tape during awriting operation, any written in error will cause the head to movelaterally on the magnetic tape when the tape is traveling straight(i.e., not moving laterally). This leads to the head moving off the datatrack and reducing the effectiveness of the writing process. Byadjusting how the servo marks are written on the magnetic tape to takeinto account tape lateral position change and tape velocity change, thewritten in error can be reduced.

FIG. 3B is an illustrative diagram of a magnetic tape 310 moving past aposition detector 308 with representative servo marks 314, 316, 318 on atape 310 designating servo marks written through different methods tocorrect for tape lateral position change and/or velocity changes.

In one approach, a servo writer 320 writes servo marks to the tape whilethe position detector 308 detects the position of the tape relative tothe servo writer. The servo writer 320 may be stationary, i.e., is notactuated, or may move. The servo writer 320 may be a standard servowriter, a pair of servo writers, etc. The position detector 308 may bean optical position detector of a type known in the art, a mechanicaldevice, etc.

For the present discussion, assume the servo writer 320 does not move.Because the servo writer 320 does not move, as the magnetic tape 310changes position laterally, the servo marks are recorded on the magnetictape closer or farther from the tape edge 312. To compensate for thispositional change, as detected by the optical position detector 308, thespacing of the servo marks is adjusted such that, if a servo reader wereto be constantly positioned at a distance d from the edge of the tapemoving at a constant velocity, the spacing of the marks would appear tothe servo sensor to be uniformly written under near-perfect conditions.For example, when the servo writer head is stationary during the servowriting operation, a timing control may be used to write the servo marksin the correct relative location on the magnetic tape to provide theforegoing effect.

Servo marks 316 are illustrative of marks that would be recorded tocompensate for tape lateral movement that causes the servo writer towrite the servo marks farther from the tape edge 312 than normal. Tocompensate for this positional change, the servo marks 316 are recordedslightly farther apart, so that when they are read by a servo reader inanother operation, they direct the read head to travel straight insteadof moving laterally to follow conventionally written servo marks.Likewise, servo marks 318 are illustrative of marks that would berecorded to compensate for tape lateral movement that causes the head towrite the servo marks closer to the tape edge 312 than normal. Servomarks 314 are illustrative of normal marks written the proper distancefrom the tape edge 312.

In one approach, the distance between a base set, a, is increased tocompensate for the tape 310 moving laterally causing the head to writethe servo marks 316 farther from the tape edge 312 than normal.

In another approach, the distance between a base set, a, is decreased tocompensate for the tape 310 moving laterally causing the head to writethe servo marks 318 closer to the tape edge 312 than normal.

In another approach, a servo pattern may be “reconditioned.” Forexample, a conventional servo written magnetic tape containing highfrequency written in noise may be used. The servo pattern on thismagnetic tape is mechanically tracked relative to the edge of the tape,and the servo pattern is analyzed to detect the written in component. Inanother approach, two or more servo readers could be used to accomplishthe measuring by taking two position readings, and then correlating thelateral position measurements to deduce the written in component. Aservo pattern with reduced written in noise may then be written over theexisting servo pattern on the magnetic tape entirely or just on andaround the portions of the servo pattern which have written in noisedetected.

An advantage of writing a servo pattern 314 that appears to a tape drivesystem to follow the tape edge 312 precisely is increased bandwidth,since mechanical head motion is reduced or eliminated during a datawriting operation. Also, hard edge guiding and associated high frequencylateral motion noise is reduced or eliminated.

In another embodiment, a servo pattern is repeatedly subjected toreading and rewriting operations to produce a more and more accurateservo pattern which appears to the system to follow the tape edge moreprecisely.

The servo track may have data embedded or encoded therein. Such data mayinclude data for encryption, for ascertaining a longitudinal positionalong the tape, etc. In one embodiment, the servo marks are written witha given height, and then an optional operation is performed to trim theservo marks to a desired height by using an erase head. The height ismeasured in a direction perpendicular to a length of the tape andparallel to the plane of the writing surface of the tape (e.g., in the ydirection of FIG. 3A).

A small height of the data bands also provides more immunity toread/write problems associated with tape dimensional instability, i.e.,lateral expansion.

FIG. 4 illustrates a simplified tape drive 400 of a tape-based datastorage system, which may be employed in the context of the presentinvention. While one specific implementation of a tape drive is shown inFIG. 4, it should be noted that the embodiments described herein may beimplemented in the context of any type of tape drive system.

As shown, a tape supply cartridge 420 and a take-up reel 421 areprovided to support a tape 422. One or more of the reels may form partof a removable cassette and are not necessarily part of the system 400.The tape drive, such as that illustrated in FIG. 4, may further includedrive motor(s) to drive the tape supply cartridge 420 and the take-upreel 421 to move the tape 422 over a tape head 426 of any type.

Guides 425 guide the tape 422 across the tape head 426. Such tape head426 is in turn coupled to a controller assembly 428 via a cable 430. Thecontroller 428 typically controls head functions such as servofollowing, writing, reading, etc. The cable 430 may include read/writecircuits to transmit data to the head 426 to be recorded on the tape 422and to receive data read by the head 426 from the tape 422. An actuator432 controls position of the head 426 relative to the tape 422.

An interface may also be provided for communication between the tapedrive and a host (integral or external) to send and receive the data andfor controlling the operation of the tape drive and communicating thestatus of the tape drive to the host, all as will be understood by thoseof skill in the art.

FIG. 5 illustrates a method 500 according to one embodiment. As anoption, the present method 500 may be implemented in the context of thefunctionality and architecture of FIGS. 1-4. However, method 500 may becarried out in any desired environment. It should be noted that theaforementioned definitions may apply during the present description.

With continued reference to FIG. 5, in operation 502, a lateral positionof a magnetic tape passing over a servo writing head during a servotrack writing operation is monitored. In one preferred embodiment, thelateral position is monitored with an optical device.

In operation 504, servo marks are written to the magnetic tape, with atiming of the writing of each mark being based on the monitored positionof the magnetic tape. In one approach, each servo mark is individuallywritten to the magnetic tape, rather than in pairs or groups. In anotherapproach, pairs or groups of servo marks may be written simultaneouslywhich may ensure a certain distance between the servo marks writtensimultaneously.

In one approach, the head containing the writers does not move duringoperation 504 or it moves to adjust for lateral position changes in thetape.

In another embodiment, a velocity of the magnetic tape is monitoredrelative to the head, wherein the timing of the writing of each mark isfurther based on the monitored velocity of the magnetic tape. Thevelocity of the magnetic tape can be monitored by an optical speeddetector, by tracking the spindle speed feeding the magnetic tape, etc.

Another approach further comprises subsequently reducing a height of thewritten servo marks, the height of the written servo marks beingmeasured in a direction perpendicular to a direction of tape travel.

In another approach, the head may be stationary during the servo writingoperation or moved laterally during servo writing operation. When thehead is stationary during the servo writing operation, the timingcontrol is used to write the servo marks in the correct relativelocation on the magnetic tape.

In another approach, the servo marks may comprise a series ofmagnetically defined bars. Also, the servo track may comprise a seriesof base sets of magnetically defined bars. Each base set could comprisetwo, three, four or more bars, with at least two bars oriented atdifferent angles with respect to a direction of tape travel. Further, anangle between at least some of the bars could be greater than 0 degreesand less than 180 degrees. Alternatively, an angle between at least someof the bars could be less than about 50 degrees, e.g., 0-50 degrees,10-40 degrees, etc.

In another approach, multiple servo tracks may be written, where adistance between the servo tracks may be less than about 3 mm, e.g.,3±0.25 mm; less than about 1.5 mm; less than about 0.75 mm; less thanabout 0.5 mm; etc., though could be higher as well.

In a further approach, one of the servo tracks may have data encodedtherein. Another approach optically monitors the lateral position of themagnetic tape.

FIG. 6 illustrates a method 600 according to one embodiment. As anoption, the present method 600 may be implemented in the context of thefunctionality and architecture of FIGS. 1-4. However, method 600 may becarried out in any desired environment. It should be noted that theaforementioned definitions may apply during the present description.

With continued reference to FIG. 6, in operation 602, a lateral positionof a magnetic tape passing over a servo writing head during a servotrack writing operation is optically monitored. Any optical devicecapable of tracking the lateral position of the magnetic tape can beused to optically monitor the lateral position of the magnetic tape.

In operation 604, a velocity of the magnetic tape relative to the headis monitored. A speed sensing device can be used to monitor the velocityof the magnetic tape, such as a radio transmitting speed gun, lasertransmitting speed gun, optical speed detector, spindle speed, etc.

In operation 606, servo marks are written to the magnetic tape, whereinthe servo marks are magnetically defined bars arranged in base sets,each base set comprising at least two bars oriented at different angleswith respect to a direction of tape travel. In this operation, the basesets of bars may contain 2, 3, 4 or more bars in each set.

In operation 608, the timing of the writing of each mark is adjustedbased on the monitored position of the magnetic tape. In one embodiment,the marks are spaced slightly farther apart when the servo marks areplaced farther from the tape edge, and are placed slightly closertogether when the servo marks are placed closer to the tape edge.

In operation 610, the timing of the writing of each mark is furtheradjusted based on the monitored velocity of the magnetic tape. Thevelocity can be monitored by an optical device, spindle speed feedingthe magnetic tape, etc.

In another approach, each servo mark is written individually to themagnetic tape. In other approaches, pairs or groups of servo marks maybe simultaneously written to the magnetic tape.

FIG. 7 illustrates a method 700 according to one embodiment. As anoption, the present method 700 may be implemented in the context of thefunctionality and architecture of FIGS. 1-4. However, method 700 may becarried out in any desired environment. It should be noted that theaforementioned definitions may apply during the present description.

With continued reference to FIG. 7, in operation 702, a previouslywritten servo pattern on a magnetic tape is read. This previouslywritten servo pattern could have been made according to the foregoingdescription, or the magnetic tape could have the servo pattern on itbefore coming into contact with this embodiment.

In operation 704, a lateral position of a magnetic tape is monitoredduring a reading operation. Any lateral position of a magnetic tape madebe monitored, and examples include monitoring the inside edge of themagnetic tape, outside edge of the magnetic tape, the position of thedata bands on the magnetic tape, etc. Any device capable of monitoringthe lateral position can be used to do so including an optical positionmonitor, mechanical position monitor, etc.

In operation 706, written in noise in the servo pattern is deduced.Written in noise can occur due to the magnetic tape moving laterallywhen the servo pattern is written, velocity of the magnetic tapechanging while writing the servo pattern, etc.

In operation 708, servo marks are written to the magnetic tape over thewritten in noise. When writing over the written in noise with new servomarks, only the portions of the servo pattern that are affected bywritten in noise may be written over, or those portions affected bywritten in noise and the surrounding areas may be written over, or allof the servo pattern may be written over with new servo marks.

In one particularly preferred approach, the system or method implementsa servo write head such as that described in U.S. Pat. No. 8,310,784 toBiskeborn et al., which is herein incorporated by reference.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. Magnetic tape media, comprising: a servo trackhaving a plurality of servo marks therealong, wherein a distance of theservo marks, as originally written, from an edge of the tape mediavaries along the length of the magnetic tape media, wherein the servomarks comprise a series of base sets of magnetically defined bars,wherein distances between otherwise identical groups of base sets isdifferent along a length of the magnetic tape media.
 2. The magnetictape media as recited in claim 1, wherein each servo mark isindividually written.
 3. The magnetic tape media as recited in claim 1,wherein the servo marks comprise a series of magnetically defined bars.4. The magnetic tape media as recited in claim 3, wherein the servomarks comprise a series of base sets of magnetically defined bars, eachbase set comprising two bars oriented at different angles with respectto a length of the magnetic tape media.
 5. The magnetic tape media asrecited in claim 4, wherein each of the servo marks in each of the basesets is individually written with respect to all other servo marks onthe magnetic tape media.
 6. The magnetic tape media as recited in claim4, wherein each of the servo marks in each of the base sets isindividually written with respect to all other servo marks in the seriesof base sets of magnetically defined bars.
 7. The magnetic tape media asrecited in claim 3, wherein the servo marks comprise a series of basesets of magnetically defined bars, each base set comprising three bars,each base set comprising at least two bars oriented at different angleswith respect to a direction of tape travel.
 8. The magnetic tape mediaas recited in claim 3, wherein the servo marks comprise a series of basesets of magnetically defined bars, each base set comprising at leastfour bars, each base set comprising at least two bars oriented atdifferent angles with respect to a direction of tape travel.
 9. Themagnetic tape media as recited in claim 3, wherein an angle between atleast some of the bars is greater than 0 degrees and less than 180degrees.
 10. The magnetic tape media as recited in claim 3, wherein anangle between at least some of the bars is less than about 50 degrees.11. The magnetic tape media as recited in claim 1, wherein at leastthree servo tracks are present on the magnetic tape media, wherein adistance between the servo tracks is less than about 3 mm.
 12. Themagnetic tape media as recited in claim 1, wherein multiple servo tracksare present on the magnetic tape media, wherein a distance between theservo tracks is less than about 1.5 mm.
 13. The magnetic tape media asrecited in claim 1, wherein multiple servo tracks are present on themagnetic tape media, wherein the distance between the servo tracks isless than about 0.75 mm.
 14. The magnetic tape media as recited in claim1, wherein at least three servo tracks are present on the magnetic tapemedia, wherein at least one the servo tracks has data encoded therein.15. The magnetic tape media as recited in claim 1, wherein the servomarks comprise a series of magnetically defined bars.